Biocontrol: Managing Mold and Contamination

In the wild, slime molds live in a “Biological War Zone.” They are surrounded by billions of fungi and bacteria competing for the same resources. In your lab, you are the general in charge of their defense.

Here is how to identify and eliminate the most common “bad actors.”

1. The Fungal Invaders

Common household molds like Aspergillus and Penicillium are your main rivals.

• Look for: White fuzz, green hair, or black “dots” growing on your oats.
• The Threat: These fungi grow faster than the slime mold in high-nutrient environments. They can “choke” the plasmodium and steal all the oxygen.
• The Tactic: Starvation. Slime molds can survive without food much longer than these molds. If you see a fungal breakout, stop feeding for 48 hours. Let the blob “pull away” from the contaminated area.

2. The Bacterial Sludge

Bacterial contamination is usually invisible until it’s too late.

• Look for: A foul, sour, or “rotting” smell. Look for “cloudy,” slimy patches that don’t have the distinct yellow veins of your blob.
• The Threat: Bacteria can produce toxic byproducts that poison the blob’s cytoplasm.
• The Tactic: Isolation. Move a small, clean piece of your blob to a fresh plate of Water Agar (WA). Because WA has no food, the bacteria will die out while the blob continues to explore.

3. The Lab’s Chemicals

• 70% Ethanol / Isopropyl Alcohol: Use this to “mist” your working area. It kills most airborne spores and surface bacteria instantly.
• 10% Bleach (Sodium Hypochlorite): This is for Total Elimination. If a dish is completely overrun by mold, do not open it. Inject a bit of bleach or soak the whole things for 2 hours before disposal.

4. Why Slime Molds are Tough

Research has shown that slime molds aren’t helpless. They secrete their own natural antibiotics and antifungals as they move.

• Bio-Cleaning: As the blob moves across the agar, it “vacuums” up bacteria.
• The Habitat: This is why Non-Nutrient Agar is so effective—it creates a world where only the blob (which carries its own energy) can survive, while the food-less competitors starve.

5. Summary Checklist for a Clean Culture

1. Always wipe your hands and tools with 70% alcohol.
2. Never leave the petri dish lid open for more than a few seconds.
3. Always remove old, uneaten oats before adding new ones.
4. Use distilled water to avoid chlorine or metallic contamination.

Final Manual Rule: If your blob turns brown and smelly, it’s likely a bacterial infection. Don’t try to save the whole plate—take a tiny, clean yellow tip and move it to a new home immediately.

Want to learn how to store your “Clean Strains” for years? See the Sclerotium Banking Guide.